Trichloroethylene risk assessment: A review and commentary

• Published in: Critical reviews in toxicology Vol. 39; no. 9; pp. 782 - 797
• Main Authors: Jollow, David J., Bruckner, James V., McMillan, David C., Fisher, Jeffrey W., Hoel, David G., Mohr, Lawrence C.
• Format: Journal Article
• Language: English
• Published: London Informa UK Ltd 01-10-2009; Taylor & Francis; Informa Healthcare
• Subjects: Animals; Biological and medical sciences; carcinogenesis; Carcinogenesis, carcinogens and anticarcinogens; Chemical agents; Chemical and industrial products toxicology. Toxic occupational diseases; Environmental Exposure - adverse effects; Humans; Medical sciences; Models, Biological; Neoplasms - chemically induced; Neoplasms - epidemiology; PBPK modeling; peroxisome proliferation; presystemic elimination; Risk Assessment; Solvents; Toxicology; Trichloroethylene; Trichloroethylene - pharmacokinetics; Trichloroethylene - toxicity; Tumors; Water Pollutants, Chemical - pharmacokinetics; Water Pollutants, Chemical - toxicity; Human; risk assessment; Toxicity; Elimination; Trichloroethylene; Review; Peroxisome proliferator; PBPK modeling; presystemic elimination; Ethylene derivatives; Toxicokinetics; Organic solvent; Carcinogen; Compartmental model; General anesthetic; carcinogenesis; Chlorine Organic compounds; Animal; Risk factor; peroxisome proliferation; Physiologically based pharmacokinetic model; Bibliographic review; Ethylene(trichloro)
• ISSN: 1040-8444; 1547-6898
• DOI: 10.3109/10408440903222177

Trichloroethylene (TCE) is a widespread environmental contaminant that is carcinogenic when given in high, chronic doses to certain strains of mice and rats. The capacity of TCE to cause cancer in humans is less clear. The current maximum contaminant level (MCL) of 5 ppb (μg/L) is based on an US Environment Protection Agency (USEPA) policy decision rather than the underlying science. In view of major advances in understanding the etiology and mechanisms of chemically induced cancer, USEPA began in the late 1990s to revise its guidelines for cancer risk assessment. TCE was chosen as the pilot chemical. The USEPA (2005) final guidelines emphasized a "weight-of-evidence" approach with consideration of dose-response relationships, modes of action, and metabolic/toxicokinetic processes. Where adequate data are available to support reversible binding of the carcinogenic moiety to biological receptors as the initiating event (i.e., a threshold exists), a nonlinear approach is to be used. Otherwise, the default assumption of a linear (i.e., nonthreshold) dose-response is utilized. When validated physiologically based pharmacokinetic (PBPK) models are available, they are to be used to predict internal dosimetry as the basis for species and dose extrapolations. The present article reviews pertinent literature and discusses areas where research may resolve some outstanding issues and facilitate the reassessment process. Key research needs are proposed, including role of dichloroacetic acid (DCA) in TCE-induced liver tumorigenesis in humans; extension of current PBPK models to predict target organ deposition of trichloroacetic acid (TCA) and DCA in humans ingesting TCE in drinking water; use of human hepatocytes to ascertain metabolic rate constants for use in PBPK models that incorporate variability in metabolism of TCE by potentially sensitive subpopulations; measurement of the efficiency of first-pass elimination of trace levels of TCE in drinking water; and assessment of exogenous factors' (e.g., alcohol, drugs) ability to alter metabolic activation and risks at such low-level exposure.